1. Field of the Invention
The present invention relates to a CMOS image sensor and other photo detecting devices.
2. Description of the Related Art
In recent years, CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) image sensors are used in a great deal of image pickup apparatuses, such as digital still cameras and digital video cameras.
A number of benefits can be gained by choosing a CMOS image sensor. For example, a CMOS image sensor can be produced on the same manufacturing line as general chips, and it can be packaged into a single chip together with the peripheral functions. Further, the CMOS image sensor is advantageous in that the CMOS image sensor can be driven at lower voltage than a CCD type and the CMOS image sensor consumes less power than the CCD type.
Each pixel of a CMOS sensor has a structure including a photodiode and a switch using MOSFETs. A solid-state image sensor equipped with an overflow drain that sweeps out an excess charge occurring in the photodiode has been proposed. When the overflow drain is provided, the charge amount stored can be increased and therefore a wider dynamic range can be achieved.
However, the provision of an overflow drain capacity in the pixel circuit increases the area of pixel circuits. Since low-cost image sensors need to be supplied for use in vehicles, there is an increasing demand of suppressing the increase in the area by the overflow drain capacity.